1. Field of the Invention:
This invention relates to a valving apparatus for use in a subterranean well, and particularly an apparatus for selectively sealing an annulus defined between the exterior of a work string and the interior of an operative element contained in a production string, such as a safety valve.
2. Description of the Prior Art:
Prior to placing any well into production, there are a number of operative elements incorporated in the production string. For example, one or more safety valves may be located at different depths along the production string. It often happens that chemical treatment, flushing or similar operations must be accomplished on the production formation, the gravel pack or the screen. Many such operations are accomplished by inserting into the bore of the production string a length of continuous tubing sometimes called "macaroni" tubing or lengths of sand washing tubing which will conduct flushing or treating fluids to the area of the well requiring attention. Such tubing may pass through one or more safety valves incorporated in the production string, and the presence of such tubing effectively prevents the closing of the safety valve until the tubing is withdrawn.
As is well known to those skilled in the art, and has been recognized by various governmental safety regulations governing the treatment of repair of wells, if the safety valve is to be blocked from closing by the passage of any work string therethrough, it is commonly required that the well be killed before the treatment operation can proceed. This is obviously a time consuming and expensive operation.